The present invention relates to exercise equipment and in particular to equipment generally utilized for anaerobic or muscular exercise, wherein for operation an exerciser applies muscular force in opposition to a resistant, or resisting, mechanical force generated in the device.
As resistance is overcome by muscle power, the muscle generally either contracts or lengthens the extension of a body limb, for example a leg or arm. In one form of muscle exercise, isometric exercise, there is no actual substantial change in limb extension during the exercise, rather the muscle is statically stressed at maximum effort for several seconds. Such methods of exercise are widely known and used, but suffer from the limitation that no single isometric exercise effectively stresses a muscle group through its full range of motion
To fully exercise a muscle group, in many instances isokinetic-type exercises are preferred. For these exercises the exerciser exerts muscle effort for a relatively long period of time and, the muscle group, by extension or contraction of the related limb, is placed under stress through its essentially full range of motion. For example, certain arm muscles might be exercised from complete contraction to full extension of the arm, as by a typical bench press or arm curl with weights or weight machines.
Maximum advantage in applying force is usually obtained, for a muscle group, near full extension of the limb involved. That is, for certain exercises, as human exercisers fully extend the exercised limb, their ability to apply force increases and the amount of force which may be applied may also increase. As an example, consider a person lying upon a weight bench doing bench presses with a typical weight bar. When the bar is supported close to the person's chest, the arms are nearly fully contracted and the exerciser has difficulty lifting the bar due to the mechanics of the human arm. However, as the arms near full extension, the arms become extended, and movement of the bar becomes easier. Thus, lifting the weight becomes easier for the exerciser as the weight is raised. As a result, for a given weight, the arms may not be exercised as fully near full extension, since the effort which must be expended is not as much of a strain on the exerciser. If the weight would be heavy enough so that strain near full extension would be great, it is possible that the weight would be too heavy to initially be lifted from the chest.
Exercise machines have been developed to provide for an increase in the amount of exertion required, as the limb is extended. For example, in exercise machines simulating bench presses of weights, the operator may move a bar or handle grip with resistance provided by heavy weights. Camming mechanisms have been developed to decrease the mechanical advantage given by the machine to the exerciser as the bar or grip is moved by the exerciser's arm extension. Thus, as the arms of the exerciser extend, it is made mechanically more difficult to move the bar or grip, and the weights become harder to move.
While such devices have been in some ways effective, they suffer from serious problems. First, they are large and bulky, and often very heavy due to the presence of the weights. Secondly, adjustments in the weights may be necessary, in order for the device to be utilizable by numerous persons of different physical abilities, and such changes can be cumbersome. Further, the cams might not always effectively match, or correlate with, the change in the exerciser's ability to impart force during an exercise stroke. Further, for such a correlation to be most effective, numerous cams may be necessary if the device is to be utilized for exercise of different muscle groups, or by different persons.
Another problem with such devices, or the use of conventional weights, is one of safety and convenience. Typically, the exerciser is lifting weights by means of a bar or lever and if muscle exertion is lessened, the weights will force movement of the bar or lever in the opposite direction. If such a motion should occur rapidly, injury could result. For example, the bar could rapidly, and with great force, fall, driven by the weights, and crush the exerciser. Further, it is difficult for a person exercising by such methods to stop in the middle of an exercise stroke, as the weights must be returned to a resting position.
Muscles generally work in pairs. These pairs are not normally balanced, but sometimes it may be desirable to exercise them approximately equally in order to avoid proportional imbalance. For example, there is a group of muscles which permit an arm to be extended, along with a correlating group which permit it to be bent or retracted. It is readily seen that for many exercise routines involving conventional utilization of weights or weight type machines, only exercise of one of a pair of muscle groups is involved. For example, in the typical bench press, the muscle group involving extension of the arms might be exercised, however since the weights tend to fall by themselves, there is no significant chance to exercise the muscle group which pulls the arms toward the chest, in contraction. In some applications, however, it may be preferable to have an exercise apparatus capable, during the same sequence, of accomodating exercising both muscle groups in a set of muscle pairs.